1. Field of the Invention
The present invention relates to the electronic control of glass forming machines and more particularly, to the precise and programmable control over at least some of the components of an individual section glass forming machine.
2. Description of the Prior Art
Typically a glass forming machine comprises a plurality of individual sections which perform identical functions only at a phase differential between each other. Each section includes a plurality of cyclically moving components which are pneumatically activated to perform the respective steps in a glass forming process. Although the basic glass forming steps have undergone very little change over the past decades, highly sophisticated control systems have evolved to control the execution of these steps thereby allowing increased production speed, greater reliability, reduced waste, closer tolerances in produced ware and greater speed in setting up a machine for a change in job.
One aspect all individual section machines have in common is that the pneumatically activated components are controlled through a plurality of associated valves which are generally located in a valve block. The activation of the valves in the block has typically been effected by a mechanical timing drum driven in synchronism with a gob feeding mechanism. Respective projecting cam members are disposed in annular grooves in the drum surface and mechanically cooperate with the valves to effect their respective activation and deactivation. Relative timing between events in the machine cycle are adjusted by the relative position of the respective cam members in the annular grooves. For a basic description of such a glassware forming machine, reference is made to U.S. Pat. No. 1,911,119 issued May 23, 1933 to H. W. Ingle.
Electronic sequencing of the respective elements of the glassware forming machine is now emerging. For a description of electrically controlled glassware forming machinery reference is made to U.S. Pat. No. 3,762,907, issued Oct. 2, 1973 to Quinn and Kwiatkowski, and U.S. Pat. No. Re. 29,642, reissued May 23, 1978 to Kwiatkowski and Wood (both commonly assigned with the present invention). Briefly, in electronically controlled glassware forming machines activation signals are generated by an electronic controller to selectively activate or deactivate solenoid operated valves to effect timed operation of the components which perform the glassware forming steps. These electronic controllers provide much more precision in the respective time in a cycle that a valve is activated and allow small adjustments in such times to be easily made. Also job changes, where the complete timing of almost all components is altered, are quickly and easily made. The more sophisticated modern controllers function similarly to these controllers but use digital computers to further enhance operator interface with the machine and provide a variety of other convenience features. Although the glass forming art has been considerably forwarded by such devices, their main limitation is that they can only provide an activation or deactivation signal at a given time in a cycle. They exert no control over the actual motion envelope of the respective component.
As those skilled in the art will appreciate, there are certain steps in the glass forming process where the motion of the component must be precisely controlled if acceptable ware is to be produced. Furthermore, the desired motion of such components may vary depending on the job. For example the invert of a parison from the blank side to the mould side must be smoothly accomplished at a given speed or the acceleration forces on the parison will result in a deformation of the soft glass. Bigger ware requires a slower speed as the centrifugal forces are greater, and a job change from smaller to bigger ware will require a change in the speed of the component which effects the revert step.
Presently, the motion envelope is controlled to a great extent through dampening of the individual pneumatic cylinders and by controlling the flow of air from the cylinders on their exhaust strokes to limit their speed of movement. One method of speed control is executed in the valve block. Activation of a solenoid valve allows air to flow through a one-way check valve in the valve block to the pneumatic cylinder thereby extending the cylinder. When the valve is deactivated and the component is returned to its original position, the one-way check valve closes and the air is forced to flow through an adjustable needle valve in the valve block. The needle valve may be adjusted to limit the flow of air from the pneumatic cylinder on the exhaust stroke and correspondingly limit the speed of the cylinder. Many of the components on a glass forming machine are activated through double-acting cylinders. The speed of such components is also affected by the air pressure connected to the valve. An example of a state of the art valve block which is adapted for electronic control is disclosed in Lowe, U.S. Pat. No. 4,293,004 which is herein incorporated by reference. The Lowe patent is commonly assigned with the present invention. A novel approach to regulating air pressure into the cylinder and the flow or exhaust is illustrated in FIG. 1 of the Lowe patent.
Although the Lowe valve block and other similar arrangements in conjunction with individual dampening of the respective pneumatic cylinders and electronic control allow a great deal of control over the motion envelope of a given component, they have a number of drawbacks. Any changes in the range of motion of a component, although rare, must still be individually adjusted at the machine. The controller and valve block can only turn an air supply on and off and limit the flow of air in and out of a cylinder. The acceleration, deceleration and velocity of a component must be adjusted by on-the-spot trial and error. Job changes requiring a change in the motion envelope of a component require a large degree of experimentation by the operator. Due to the large volume of air flow even a single forming machine uses it is often desirable to operate with unfiltered air. In the typical operation of the I.S. machine various condensation, cylinder oil, sludge and varnish from the compressor tend to find their way into the air lines. Such foreign materials may play havoc with the fine adjustment of a needle valve requiring constant operator adjustment of speed for some critical components.
Perhaps most importantly, it is thought that precise control over the motion envelopes of at least some of the more critical components of a glass forming machine will allow further increases in production speed, a further reduction in waste or defectively produced containers, and possibly breakthroughs in lightweight container technology.